Refractory alloy



United States Patent C) 3,329,498 REFRACTORY ALLOY Gilbert Cavalier,Saint-Germain-en-Laye, France, assignor to Institut de Recherches de laSiderurgie, Saint-Germain-en-Laye, France No Drawing. Filed Jan. 27,1966, Ser. No. 523,256 Claims priority, application France, Nov. 9,1962, 914,915 10 Claims. (Cl. 75-170) The present application is acontinuation-in-part of my copending application, Ser. No. 319,469,filed Oct. 28, 1963, and entitled Refractory Alloy, now abandoned.

The present invention relates to an alloy and, more particularly, to anon-ferrous alloy which at relatively high temperatures will resistoxidation and possess a high creep strength.

It is an object of the present invention to provide an alloy which attemperatures of at least 1400 C., and even higher, possesses sufficientcreep strength and resistance to oxidation so as to be suitable for usein the construction of heating elements for electrical furnaces, or forcastings which will resist the action of oxidizing agents and maintaintheir strength at elevated temperatures. Alloys according to the presentinvention give excellent results even when used at temperatures above1500 C.

It is a further object of the present invention to provide an alloyWhich in addition to the above-described qualities also possesses asufficiently low electric resistivity so that it can be used in themanufacture of induction heating elements.

The majority of alloys available up to now for the above-indicatedpurposes are of such quality that, for instance, induction heatingelements made thereof cannot be used at temperatures exceeding 1350 C.and thus, the alloy of the present invention because of its high creepstrength and resistance to oxidation even at temperatures of 1400 C. orhigher is particularly suitable for the manufacture thereof of heatingelements for electromagnetic induction heating devices.

Other objects and advantages of the present invention will becomeapparent from a further reading of the description and of the appendedclaims.

With the above and other objects in view, the present inventioncontemplates a highly temperature resistant alloy, the alloy consistingessentially of 21% to 35% aluminum, to 4% copper, 0% to 4% of at leastone metal selected from the group consisting of tungsten, molybdenum,vanadium and chromium, the balance being at least one metal selectedfrom the group consisting of nickel and cobalt, wherein in the absenceof copper said at least one metal selected from the group consisting oftungsten, molybdenum, vanadium and chromium is present in an amount ofat least 0.2%, and in the absence of said at least one metal selectedfrom the group con sisting of tungsten, molybdenum, vanadium andchromium said copper is present in an amount of at least 0.2%.

Surprisingly it has been found that the heat resistance of alloysaccording to the present invention significantly exceeds the heatresistance of alloys conventionally used for similar purposes. Thealloys according to the present invention include the following rangesof composition wherein, as throughout this specification, all percentagefigures are percent by weight: 21 to 35 percent of aluminium, 0.2 to 4percent of copper and the remainder principally at least one of themetals nickel and cobalt; Preferably and especially for the mosteffective alloys, the composition should be kept within the ranges 21.8to 32.8 percent aluminium, 0.2 to 4 percent copper and the remainder atleast one of nickel and cobalt.

3,329,498 Patented July 4, 1967 It has been discovered also that anequally good performance may be obtained by employing in combinationwith the aluminium and one or both of nickel and cobalt, one or more ofMo, W, V and Cr in amounts of 0.2 to 4 percent. Excellent results arealso obtainable when employing 21 to 35 percent aluminium and 0.1 to 4percent copper along with 0.1 to 4 percent of one or more of the metalsMo, W, V and Cr.

Thus, broadly, the present invention is concerned with a refractory,non-ferrous alloy which comprises at least three metals, namely aluminumwith or without Cu and at least one metal each of the two groupsdescribed above.

According to one preferred embodiment, the alloy of the presentinvention is composed of aluminum, nickel and copper and containsbetween 21.8% and 32.8% of aluminum; between 67% and 78% of nickel; andbetween 0.2% and 4% of copper.

According to another preferred embodiment, the alloy of the presentinvention is composed of aluminum, cobalt and copper and containsaluminum in an amount of between 2l.8% and 32.8%; cobalt in an amount ofbetween 67% and 78%; and copper in an amount of between 0.2% and 4%.

Another preferred alloy according to the present invention is composedof a mixture in any proportion of the aluminum nickel copper alloy andthe aluminum cobalt copper alloy described above.

Mention has been made above that the greater portion of the alloy isprincipally one or more of nickel and cobalt. This is noted specificallybecause, while desiring the purest raw materials in the production ofthese hightemperature alloys there is some limited permissibility ofimpurities and remainders of deoxidizing additions such as Fe, Mg, Si,Mn, etc. In general the total of such elements should not exceed onepercent.

The alloy of the present invention may contain inclusions of oxides ofits constituents, particularly of mixed oxides, for instance of A1 0 andNiO, or A1 0 and C00. These oxides may develop or be developed duringthe course of melting and alloying or subsequently by exposure to anoxidizing atmosphere at elevated temperature. Specifically, good resultshave been obtained with a total oxide content of up to 1000 ppm. in theform of such mixed oxides.

The copper in all of the above-described compositions may be completelyor partially replaced by one or more of the metals molybdenum, tungsten,vanadium and chromium within the indicated proportions. Thus, accordingto another preferred embodiment of the present invention, the alloycontains in addition to aluminium and nickel or cobalt, copper and atleast one of the metals molybdenum, tungsten, vanadium and chromium.

The alloys of the present invention may be advantageously produced by amethod according to which first the aluminium and copper are meltedtogether and thereafter the remaining constituents of the alloy aresuccessively introduced while simultaneously the temperature of themolten metal is raised. The operation is advantageously effected in anoxidizing atmosphere. If there are more than one remaining constituentto be introduced, then these remaining constituents preferably areintroduced in such sequence that the melting point of the molten metalmixture is prorgessively raised by the introduction of the remainingconstituents.

It will be understood that the alloy according to the present inventionmay be considered a derivative of stoichiometric alloys of aluminiumwith nickel and/or cobalt. However, it is known that such alloys,consisting essentially of two constituents, due to their highbrittleness are not suitable for industrial use at high temperatures.

By introducing, in accordance with the present invention, at least athird or also a fourth or more constituents, i.e., by forming forinstance a ternary or quaternary alloy of the qualitative andquantitative composition described above, an alloy is obtained whichpossesses the resistance to oxidation which is shown by theabove-mentioned binary, stoichiometric alloy, but very importantlyovercoming the brittleness of this stoichiomertic alloy. Furthermore, bythe inclusion of oxides of such constituents, the creep strength of thealloy is improved.

The alloy of the present invention is preferably prepared by firstmelting the most fusible constituents of the alloy together andthereafter, in a second melting stage, to add the other constituents,particularly cobalt and/ or nickel, at a higher temperature, duringwhich secnd stage the metal is homogenized by stirring. The process ofthe present invention is efiiciently performed by heating the alloyconstituents by induction. As the alloy is produced in the presence ofan oxidizing atmosphere, such as air, oxides of aluminum and nickel and/or cobalt, mainly mixed oxides of the type Al,O NiO or will be formedand remain in the alloy.

No care will be exerted to eliminate such oxides as they are notdetrimental to the good qualities of the alloy and give it excellentmechanical properties at high temperature.

Within the broad range of maximum and minimum percentages of theindividual constituents of the alloy of the present invention, alloyswill be obtained suitable for use at a maximum working temperature of atleast 1400 C., while alloys within the percentage limits of thepreferred ranges will be suitable for industrial use at temperatures of1500 C. and even higher.

The following examples are given as illustrative only, without limitingthe invention to the specific details of the examples.

Example 1 In an induction heated crucible in contact with thesurrounding air, a liquid alloy is produced composed of 30% A1, 69% Ni,1% Cu and 900 p.p.m. of oxides of these metals. With the help of aquartz tube of 4 mm. diameter which is subjected to a progressivepartial vacuum, several samples are lifted from the metal bath in theform of small bars.

The thus-formed small bar is heated to 1535 C. and thereafter, whilethis temperature is maintained, an electric current of 315 amperes and1.56 volts is passed through the bar for a period of 169 hours duringwhich no recognizable change takes place in the bar. Particularly theweight of the bar does not change in an appreciable manner which provesthat the metal is not oxidized except possibly to an extremely lowdegree. The resistivity of the alloy at 1535 C. was determined to be49.5 X ohm-centimeter.

Example 2 An alloy of the composition Al 29%, Co 70%, Cu 1%, andcontaining 800 p.p.m. of oxides of these metals is produced in a heatedcrucible in contact with the surrounding air. In the manner described inExample 1, small sample bars are withdrawn from the molten metal.

The sample bars are then heated at 1620 C. and at that temperature anelectric current of 315 amperes is passed through the bars for an entireweek. Thereafter, no noticeable change is found in the composition ofthe bars. Particularly their weights have not changed in an appreciablemanner.

Similar experiments were carried out with an alloy of the prior artcomposition Ni 82%, Al 17%, Cu 1%. This alloy cannot even be used in themanner described in the above examples because it starts to meltpartially upon reaching this temperature of 1400 C.

The alloy composition of the present invention is entirely novel and canbe used at temperatures which are more than 50 C. higher than those atwhich the conventional alloys lose their usefulness. The difference ofmore than 50 C. is very important and one cannot ignore that thecalories made available for heat transfer at high temper'atures areextremely valuable. It will be understood that the alloy of the presentinvention is of great interest to the industry in connection withelectric resistance heating arrangement.

Without attempting to limit the present invention to any specifictheory, it might be assumed that upon solidification of the alloy aconglomerate of crystals is formed, whereby the strength of adherence ofthe crystals to each other and thus the cohesion of the alloy will begreatly influenced by small amounts of material interposed betweenadjacent crystals.

In the case of binary alloys of aluminum and nickel or aluminum andcobalt, this interposed material will consist of small amounts of oxidesof the alloy forming metals. These oxides have very little power ofadhesion and, consequently, there will be little cohesion between thecrystals of the binary alloy.

These crystals will consist of for instance Al-Ni formed of a solidsolution which may contain an excess of either nickel or aluminum,depending on whether the nickel content is higher or lower than 68%.Similarly, Al-Co crystals are formed of the solid solution whereby,depending on whether the cobalt is present in an amount of more or lessthan 64%, an excess of nickel or cobalt will remain.

If, in accordance with the present invention, copper and/or -one or moreof the metals molybdenum, tungsten, vanadium or chromium areincorporated in the alloy, then these additional metals will be locatedat the interfaces between the Al-Ni or Al-Co crystals. Since the powerof adhesion of these additional metals in contact with the binarycrystals is much higher than that of the oxides, the presence of theseadditional metals will greatly increase the cohesion of the crystals andthus of the alloy.

In other words, the adhesive forces of the material at the interfaces ofthe crystals seem to be of decisive importance for the cohesion and thusthe mechanical characteristics in the alloy. These forces of the oxidesare small while, in contrast thereto, the metals which are added to thebinary alloy in accordance with the present invention, namely copperand/or at least one metal selected from the group consisting oftungsten, molybdenum, vanadium and chromium greatly increase thecohesive forces between the interfaces of the binary crystals.

Example 3 An alloy of the composition A1 29.5%, Ni 70%, Cr 0.5% andcontaining 850 p.p.m. of oxides of these metals is produced in aninduction heated crucible in contact with the surrounding air. In themanner described in Example 1, with the help of a quartz tube of 3.5 mm.inner diameter, several samples are lifted from the metal bath in theform of small bars.

The sample bars are then heated at 1480 C. and at that temperature, anelectric current of 270 amperes and 1.54 volts is passed through thebars for a period of 56 hours. The resistivity of the alloy calculatedat 1480 C. equals 56.8 10' ohm centimeter. No change in the condition ofthe alloy bar could be found after the above described 56 hours passageof electric current therethrough.

Example 4 An alloy of the composition: A1 30.8%, C0 68%, M0 0.4%, Cu0.8%, and containing 600 p.p.m. of oxides of these metals is produced incontact with the surrounding air. With the help of a quartz tube havingan inner diameter of 3.5 mm. and in the manner described in Ex ample 1small sample bars are withdrawn from the molten metal.

The sample bars are then heated to 1570 C. and at that temperature anelectric current of 3 30 amperes and 1.68 volts is passed through thesample bars. The resistivity of the alloy at 1570" C. is 52x10ohm-centimeter.

Example 5 An alloy of the composition: Al 30%, Ni 69%, Cu 1% and about60 p.p.m. of oxides of these metals is pro duced in a protective argonatmosphere in order to keep the oxide content as low as practicallypossible.

In the manner described in Example 4, small sample bars are withdrawnfrom the molten alloy, and the sample bars are then heated for 48 hoursat a temperature of 1520 C., during which period no recognizable changestake place in the thus heated bars.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. A high temperature resistant alloy, said alloy consisting of 21% to35% aluminum, an amount not exceeding 4% of a substance selected fromthe group consisting of copper and at least one metal selected from thegroup consisting of tungsten, molybdenum, vanadium and chromium, thebalance being at least one metal selected from the group consisting ofnickel and cobalt, wherein (a) in the absence of copper, at least onemetal selected from the group consisting of tungsten, molybdenum,vanadium and chromium is present in an amount of at least .2%,

(b) in the absence of nickel and of metals selected from the groupconsisting of tungsten, molybdenum, vanadium and chromium, said copperis present in an amount of at least .2%,

(c) in the presence of nickel, at least one of said metals selected fromthe group consisting of tungsten, molybdenum, vanadium and chromium ispresent in an amount of at least .2%, and

(d) in the simultaneous presence of copper and at least one metalselected from the group consisting of tungsten, molybdenum, vanadium andchromium, said copper and at least one metal selected from the groupconsisting of tungsten, molybdenum, vanadi- 6 um and chromium are eachpresent in an amount of at least 2%.

2. A highly temperature resistant alloy as defined i1. claim 1, andconsisting essentially of 29% aluminum, cobalt and 1% copper.

3. An alloy as defined in claim 2, and including between 800 and 1000parts per million of oxides of the metals of said alloy.

4. An alloy as defined in claim 1, and including up to about 1000 partsper million of oxides of the metals of said alloy.

5. A highly temperature resistant alloy according to claim 1, being freeof nickel and including 21.8% to 32.8% aluminum and 67% to 78% cobalt.

6. A high temperature resistant alloy, said alloy consisting of 21% to35% aluminum, between 0.2% and 4% copper, the balance being cobalt.

7. A high temperature resistant alloy, said alloy consisting of 21% to35% aluminum, between 0.2% and 4% of at least one metal selected fromthe group consisting of tungsten, molybdenum, vanadium and chromium, thebalance being nickel.

8. A high temperature resistant alloy, said alloy consisting of 21% to35% aluminum, between 0.2% and 4% of at least one metal selected fromthe group consisting of tungsten, molybdenum, vanadium and chromium, thebalance being cobalt.

9. A high temperature resistant alloy, said alloy consisting of 21% to35% aluminum, at least 0.2% of copper, at least 0.2% of a metal selectedfrom the group consisting of tungsten, molybdenum, vanadium andchromium, the combined amount of said copper and said at least one metalnot exceeding 4%, the balance being nickel.

10. A high temperature resistant alloy, said alloy consisting of 21% to35% aluminum, at least 0.2% of copper, at least 0.2% of a metal selectedfrom the group consisting of tungsten, molybdenum, vanadium andchromium, the combined amount of said copper and said at least one metalnot exceeding 4%, the balance being cobalt.

References Cited UNITED STATES PATENTS 1,612,642 12/1926 Mudge -1701,630,448 5/1927 Oertel 75-128 604,201 10/1934 Germany.

OTHER REFERENCES Alexander: Copper-Rich Nickel-Aluminum-Copper Alloys,Part II, The Constitution of the Copper-Nickel-Rich Alloys, The Journalof the Institute of Metals, vol. 63, No. 2, 1938, pages 164 and 165relied on.

DAVID L. RECK, Primary Examiner.

R, O, DEAN, Assistant Examiner.

1. A HIGH TEMPERATURE RESISTANT ALLOY, SAID ALLOY CONSISTING OF 21% TO35% ALUMINUM, AN AMOUNT NOT EXCEEDING 4% OF A SUBSTANCE SELECTED FROMTHE GROUP CONSISTING OF COPPER AND AT LEAST ONE METAL SELECTED FROM THEGROUP CONSISTING OF TUNGSTEN, MOLYBDENUM, VANADIUM AND CHROMIUM, THEBALANCE BEING AT LEAST ONE METAL SELECTED FROM THE GROUP CONSISTING OFNICKEL AND COBALT, WHEREIN (A) IN THE ABSENCE OF COPPER, AT LEAST ONEMETAL SELECTED FROM THE GROUP CONSISTING OF TUNGSTEN, MOLYBDENUM,VANADIUM AND CHROMIUM IS PRESENT IN AN AMOUNT OF AT LEAST .2%, (B) INTHE ABSENCE OF NICKEL AND OF METALS SELECTED FROM THE GROUP CONSISTINGOF TUNGSTEN, MOLYBDENUM, VANADIUM AND CHROMIUM, SAID COPPER IS PRESENTIN AN AMOUNT OF AT LEAST .2%, (C) IN THE PRESENCE OF NICKEL, AT LEASTONE OF SAID METALS SELECTED FROM THE GROUP CONSISTING OF TUNGSTEN,MOLYBDENUM, VANADIUM AND CHROMIUM IS PRESENT IN AN AMOUNT OF AT LEAST.2%, AND (D) IN THE SIMULTANEOUS PRESENCE OF COPPER AND AT LEAST ONEMETAL SELECTED FROM THE GROUP CONSISTING OF TUNGSTEN, MOLYBDENUM,VANADIUM AND CHROMIUM, SAID COPPER AND AT LEAST ONE METAL SELECTED FROMTHE GROUP CONSISTING OF TUNGSTEN, MOLYBDENUM, VANADIUM AND CRHOMIUM AREEACH PRESENT IN AN AMOUNT OF AT LEAST .2%.